curl --request POST \
  --url https://api.unibee.dev/merchant/email/send_email_to_user \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "attachInvoiceId": "<string>",
  "content": "<string>",
  "email": "<string>",
  "gatewayTemplateId": "<string>",
  "subject": "<string>",
  "variables": {}
}'

{
  "code": 123,
  "data": {},
  "message": "<string>",
  "redirect": "<string>",
  "requestId": "<string>"
}